I am going to throw some ideas out here.
Annasmom, were you able to search for ANY passport GW had, or just the one that you knew about and its replacement? Is it possible he had other passports?
Is there any proof that Brody had a passport? Any proof that he accompanied GW at any time when he went out of the country?
You state that you have no doubt that GW loved Anna, yet he abandoned you and her for a babbling idiot guru, resented paying CS, appeared to be concerned about possibly having to pay more, stopped paying CS before it was even clear if she would turn up, did not have anything to do with her, did not search for her, and took a vacation within weeks of her disappearance. I've heard nothing about him bothering to search for her at all. Heard nothing about him sending her letters, visiting or sending presents. This really does not sound to me like someone who loves or cares about a child, unless the other party is restricting their access, and you don't sound like the kind of person who would do that. The premise that he might have been involved with her abduction does not point to a person who loves their child. I admire the fact that you are pretty positive in your comments about him, but I do have to say I find it confusing. If I felt that my ex was in any way responsible for the disappearance of my child, I would despise them. I'm having a hard time understanding that.
Hmm. That thing. The fact that he immediately stopped paying CS, even though he would have no idea if she might just turn up at a house down the road or somewhere else a few weeks later, says a lot. No body had turned up. It tells me he was pretty sure she wouldn't.